Rev counter issue

[Dave1]

Talking about a 306, 1.9 td late model XUD engine

Just wondering if some could tell me where the signal for the rev counter starts. I believe it will be electronic, I know the speedo is. I guess there will be a sensor near the crank somewhere. The reason I ask is the the rev counter is working intermittently. I would rather start at what I believe would be the easy end. Checking for any dirt etc.

Any hlep or suggestions welcomed.

Thanks.

[CitroJim]

Hi Dave,

Normally the tacho signal is derived from the TDC sensor located on the top of the gearbox bellhousing. Worth checking its connector as it's ideally placed to pick up any old moisture flying around the engine bay.

If it has a Lucas or Bosch fully mechanical pump, the TDC sensor signal goes straight to the tacho head. If the car has a semi-electronic pump controlled by an ECU, the tacho signal may be derived from either the TDC sensor or the Needle Lift Sensor on No.3 injector (look to see if it has a thin black wire coming from it to a plug/socket on the top of the cylinder head) and the signal is then processed by the ECU before going to the tacho head.

If the tacho is a bit iffy because of a duff sensor on an ECU controlled pump, you'll surely have running problems to accompany it, usually a bit of a knock or generally poor running with possibly the engine management light illuminated.

[Dave1]

Thanks Jim,

That is helpful. I looked at the bellhousing earlier today but access is a bit limited. I can easily remove a few bits to see all. I did not want to wast time looking in the wrong place. I believe the pump is Lucas and fully mechanical but will check this when I next look, may be the weekend.
Engine is running well which sounds positive.

I will post back, hopefully with good news.

[Dave1]

Bit late with this reply

The sensor was under the engine, lying on your back looking up and left into the bell housing. Was pretty easy to find in the end as I bought a new one and followed the cable from the connection at the front of the engine. It is a grey block facing forwards and easily seen. There is just one nut to undo the sensor and with a bit of twisting and pulling it eventually came free.

Sorry for the very late update and thanks Jim for your help at the time.

[GingerMagic]

Hi Dave and Jim - hope you don't mind me barging in.
I stumbled across your conversation while searching the forum for clues as to why my rev-counter on my 306 td xud was working for 5 mins, then erratic, then nothing, on every journey...!!
I was advised to check the tdc sensor which I believe on mine is visable from above as it is on the top of the bellhousing - I will check underneath in the daylight -but all seems well with the wiring.
Should I just take the plunge and buy a new sensor? Rev counter is only really used by me when I thrash the car , but the wife misses itto clear out the soot before the MOT as don't want to blow it up, but the wife misses it...
Thanks for your help and input.

[Peter.N.]

The problem as already mentioned is usually in the connector, very rarely do the sensors fail. Its not easy to get at, it sits just above the gearbox bell housing at the bottom of the head - at least it has on all the XUDs I've had. Because the engine is tilted you will find it slightly toward the back of the engine, you should be able to see the connector if not the sensor.

Peter

[citronut]

i cant remember which model/year's but the usual place is as above, just below the head pointing towards the N/S at the rear of the flywheel,
this type is usually black plastic,

also some model's/year's have in the top of the bellhouseing,
this type is usually metal and might just be the petrol mode's ??????,

regards malcolm

[spider]

http://www.frenchcarforum.co.uk/forum/v ... 11&t=33023" onclick="window.open(this.href);return false;

[GingerMagic]

Thanks for that thread Andy, perhaps the wiring I am fiddling with is not the sensor after all....
I will have a good look when the rain stops.
Kelv.

[Dave1]

If it is not working I would just buy one. IIRC about £20. Very satisfying when it works again.

[GingerMagic]

I just had to Google IIRC, not sure what it was or meant - I am such a divvy. Got it now though, how I wish I was young again. Word..!!